Scheme of boosting adjustable ground level(s) of storage capacitor(s) of BJT pixel circuit(s) in pixel array circuit of image sensor apparatus

Abstract

A bipolar junction transistor (BJT) pixel circuit, including: a BJT transistor, having a base coupled to a photo detector, an emitter coupled to a shutter circuit, and a collector coupled to a reference ground level; the photo detector, having first end coupled to the base of BJT transistor and second end coupled to the reference ground level, for generating base current based on light intensity of light incident on the photo detector; the shutter circuit, coupled to the emitter of the BJT transistor, for controlling exposure time of the photo detector according to a shutter signal; and a storage capacitor, coupled between the shutter circuit and an adjustable ground level different from the reference ground level, for storing image data captured by the photo detector, wherein the adjustable ground level is boosted to be higher than the reference ground level for one or more times during the exposure time.

Description

BACKGROUND OF THE INVENTION1. Field of the Invention[0001]The invention relates to bipolar junction transistor pixel circuit, and more particularly to a bipolar junction transistor pixel circuit, a pixel array circuit, and an image sensor apparatus thereof.2. Description of the Prior Art[0002]Generally speaking, the performance of a conventional optical tracking system using a pixel circuit having a photo detector structure to sense the energy of the incident light to capture image data is limited by the environment light, the turn-on period of a shutter, or other factors associated with light source since the voltage of a storage capacitor of the pixel circuit easily becomes saturated in a situation of a higher light intensity when the storage capacitor is discharged. The quality of image contrast will be unavoidably degraded due to the voltage saturation, and thus the performance of optical tracking is worse.SUMMARY OF THE INVENTION[0003]Therefore one of the objectives of the inve...

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Benefits of technology

[0007]According to the embodiments, the image contrast of the BJT pixel units is significantly improved and thus the image quality is better. The tracking performance of the image sensor apparatus when applied to an optical tracking device / system is better compared to the conventional optical tracking device / system.

Problems solved by technology

Generally speaking, the performance of a conventional optical tracking system using a pixel circuit having a photo detector structure to sense the energy of the incident light to capture image data is limited by the environment light, the turn-on period of a shutter, or other factors associated with light source since the voltage of a storage capacitor of the pixel circuit easily becomes saturated in a situation of a higher light intensity when the storage capacitor is discharged.

The quality of image contrast will be unavoidably degraded due to the voltage saturation, and thus the performance of optical tracking is worse.

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